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[...]... than this because of the a age of the universe a long time it took to cool An estimate for the cooling time is included in the estimate for the age of the earth age of the universe A time determined by the reciprocal of the value of the *Hubble constant to be about 13.7 billion years The calculation of the Hubble constant, and hence the age of the universe, depends on which theory of *cosmology is used... aerodynamics is to the *Ûight of birds and insects The branch of aerodynamics concerned with the Ûow of gases through compressors, ducts, fans, oriÜces, etc., is called internal aerodynamics Aerodynamic drag is the force that opposes the motion of a body moving relative to a gas and is a function of the density of the gas, the square of the relative velocity, the surface area of the body, and a quantity... arrangement of the parts of a Ûower bud, especially of the sepals and petals aetiology The study of causes, especially the causes of medical conditions afferent Carrying (nerve impulses, blood, etc.) from the outer regions of a body or organ towards its centre The age of the earth term is usually applied to types of nerve Übres or blood vessels Compare efferent aÛatoxin Any of four related toxic compounds... the form of Ülaments (called thin Ülaments) Each thin Ülament consists of two chains of globular actin molecules, around which is twisted a strand of *tropomyosin and interspersed *troponin Units of muscle Übre (see sarcomere) consist of actin and *myosin Ülaments, which interact to bring about muscle contraction Actin is also found in the microÜlaments that form part of the *cytoskeleton of all cells... 1960 Algol 68, of 1968, is a more powerful abstract language The Ünal version, Algol W, was the precursor of Pascal The name is short for algorithmic language algorithm A method of solving a problem, involving a Ünite series of steps In computing practice the algorithm denotes the expression on paper of the proposed computing process (often by means of a Ûowchart) prior to the preparation of the program... larger nucleus during the course of the type of radioactive decay known as alpha decay As a helium–4 nucleus consists of two protons and two neutrons bound together as a stable entity the loss of an alpha particle involves a decrease in *nucleon number of 4 and decrease of 2 in the *atomic number, e.g the decay of a uranium–238 nucleus into a thorium–234 nucleus A stream of alpha particles is known as... pollutants that are responsible for the formation of *acid rain; nitrogen oxides also contribute to the formation of *photochemical smog See also ozone layer; pollution air sac 1 Any one of a series of thinwalled sacs in birds that are connected to the lungs and increase the efÜciency of ventilation Some of the air sacs penetrate the internal cavities of bones 2 A structural extension to the *trachea... eutrophication of water systems See also eutrophic algebra The branch of mathematics in which variable quantities and numbers are represented by symbols Statements are usually made in the form of equations, which are manipulated into convenient forms and solved according to a set of strictly logical rules algebraic sum The total of a set of quantities paying due regard to sign, e.g the algebraic sum of 3 and... the same line by the use of band separation Ülters at each telephone socket adsorbate A substance that is adsorbed on a surface adsorbent A substance on the surface of which a substance is adsorbed a adsorption a adsorption The formation of a layer of gas, liquid, or solid on the surface of a solid or, less frequently, of a liquid There are two types depending on the nature of the forces involved In... stability of salts of oxo acids increases down the group In general, salts of the alkalineearth elements are soluble if the anion has a single charge (e.g nitrates, chlorides) Most salts with a doubly charged anion (e.g carbonates, sulphates) are insoluble The solubilities of salts of a particular acid tend to decrease down the group (Solubilities of hydroxides increase for larger cations.) alkaloid One of . A Dictionary of Science FIFTH EDITION 3 1 Great Clarendon Street, Oxford ox2 6dp Oxford University Press is a department of the University of Oxford. It furthers the University’s objective of. earth’s crust, often expressed as a percentage. For ex- ample, the abundance of aluminium in the earth’s crust is about 8%. 2. The ratio of the number of atoms of a particular iso- tope of an element. physics) The conversion of the energy of electro- magnetic radiation, sound, streams of par- ticles, etc., into other forms of energy on passing through a medium. A beam of light, for instance,